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Abstract

Keggin-type phosphomolybdic acids with molybdenum partially substituted by vanadium and protons completely substituted by tellurium have been prepared, characterized and tested as catalysts in the partial oxidation of isobutane into methacrolein (MAL) and methacrylic acid (MAA). Characterization results showed that the structures of Te(1.5+0.5x)PMo12−xVxOn (x = 1–3) with Mo partially substituted by V can basically be preserved, while the XRD pattern of Te1.5PMo12On was different from H3PMo12O40. It is found that Te element induced a positive effect on the selectivity to MAL with slightly negative effect on the activity and selectivity to MAA.

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Abstract

Pt catalysts supported on Al-HMS materials having different Si/Al ratio were prepared and characterized by XRF, N2 adsorption–desorption isotherms, NH3-TPD and pyridine-adsorbed FTIR techniques. The catalytic performance of samples was investigated for the hydroisomerizaton of n-heptane in the temperature range of 250–400 °C and compared as a function of Al content. The catalytic evaluation revealed that Pt/Al-HMS catalysts had a high activity and unique selectivity to multibranched (MuB) isoheptanes. The molar ratio of MuB to monobranched isoheptanes (R) in the isomerization products varies within a very narrow range between 0.7 and 1.1, which is several times greater than those reported in the literature under similar reaction conditions using zeolite-supported catalysts. The formation of the MuB isoheptanes had a close correlation with the mesopore diameters of the catalysts.

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Abstract

The solid superacid catalysts were synthesized by loading AlCl3 on silica gel for benzene alkylation. The prepared catalysts were characterized by various techniques such as BET, FT-IR, MAS-NMR and scanning electron microscopy. The Hammett acidity function (Ho) was used to determine the acid strength of the solid catalysts by employing various Hammett indicators. These catalysts were found to be highly active for benzene alkylation with 1-dodecene. The catalyst prepared by the wet impregnation technique showed ~33% selectivity of 2-LAB and AlCl3 vapor treated silica gel catalyst (SG-AlCl3v) showed ~45% selectivity of 2-LAB. The FT-IR spectra of the SG-AlCl3v catalyst showed equal number of Br⊘nsted and Lewis acidic sites. The life of SG-AlCl3v catalyst was evaluated in a packed bed reactor and was found to be ~300 h for benzene alkylation with 1-dodecene. The 27Al MAS-NMR of SG-AlCl3v catalyst showed a band at 96.578 ppm, which is attributed to 4-coordinated Al species (2O, 2Cl). The Ho of SG-AlCl3v catalyst was found in the range of −12.70 > Ho > 13.16, indicates the superacidic nature. A nonlinear optimization algorithm was developed in MATLAB 7.4.0 and used to determine the kinetic parameters of the benzene alkylation with 1 dodecene in presence of SG-AlCl3v catalyst. The concentrations of the products predicted by the model was found in good agreement with experiments.

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Abstract

The catalytic hydrogenation of p-nitrophenol to produce p-aminophenol (PAP) was carried out over the catalyst nickel supported on active carbon (AC). The calcination temperature was one of the most important technical conditions: temperature higher than 450 °C would result in the reduction of NiO to Ni phase by AC and the loss of support. The surface area and nickel dispersion over catalyst decreased obviously after 450 °C calcination temperature because of the loss of support and the Ni phase sintering. Addition of K2O enhanced the alkalinity of the Ni/AC catalyst, and the p-nitrophenol stuff performed rather stronger acidity. Therefore, the level of p-nitrophenol adsorption over Ni/AC catalyst was improved, and the reaction efficiency was enhanced consequently. The p-nitrophenol conversion and PAP selectivity reached 97.7 and 99.3% over Ni–K2O/AC catalyst, respectively. During the process of catalytic hydrogenation, higher PAP selectivity was kept successively. It indicated that no side reactions happened during the catalytic hydrogenation of p-nitrophenol.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Viorel Chihaia, Karl Sohlberg, Karl Sohlberg, and Niculae I. Ionescu
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Reaction Kinetics, Mechanisms and Catalysis
Authors: Yunfeng Hu, Jinpeng Cao, Jun Deng, Baoyu Cui, Mingwei Tan, Junfei Li, and Hongsheng Zhang

Abstract

We investigated the reductive amination of ethanol to acetonitrile on Cu/γ-Al2O3. The different catalysts were characterized by XRF, XRD, H2-TPR and CO adsorption, and products were identified by FTIR and GC–MS. Our results show that dehydrogenation of ethanol takes place over Cu sites, γ-Al2O3 not only plays the role of the carrier and has catalytic dehydration function. Cu sites with high metal area and good stability are necessary to get high yield of acetonitrile. Among the impregnation, coprecipitation and physical mixing methods, impregnation is the most suitable to form Cu sites for meeting the requirements. The phase of copper species and the stability of Cu/γ-Al2O3 catalysts are closely related to Cu loading. With the increase of copper loading up to 15%, Cu/γ-Al2O3 shows good stability, which is more important for long period reaction. The effect of different reaction conditions such as reaction temperature, ethanol WHSV and ammonia/ethanol molar ratio were also investigated.

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Abstract

The kinetics of the oxidation of aspartic acid by peroxomonosulfate catalyzed by ruthenium(III) chloride was studied in acidic medium. The stoichiometry of the reaction corresponds to a reaction in which a mole of the amino acid reacts with a mole of peroxomonosulfate ion. A plausible reaction mechanism has been suggested and the derived rate law accounts for all experimental observations. Activation parameters have also been evaluated.

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Abstract

Experimental and density functional theory results of the oxidative addition and CO insertion steps of methyl iodide with [Rh(CH3COCHCOCF3)(CO)(P(OCH2)3CCH3)] are presented. Large negative experimental values for the activation entropy and results from a density functional theory study indicated trans addition of the CH3I to [Rh(CH3COCHCOCF3)(CO)(P(OCH2)3CCH3)]. Although the electron withdrawing CF3 group slows down the oxidative addition step, the strong electron donation of P(OCH2)3CCH3 still accelerates the oxidation addition step by ca 20 times (at 35 °C) compared to that of the Monsanto catalyst.

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Abstract

Hydroxyurea (HU) effectively reduces vanadate (VO2 +) into vanadyl (VO2+) species in acidic aqueous solution acting as a two-electron donor. The reaction starts by the formation of a transient complex followed by an electron transfer process that includes the formation and subsequent fading out of a free radical, U (U≡H2N–C(=O)N(H)O). The rate determining step of the redox reaction is the formation of a free radical either by the inner-sphere one-electron transfer within the formed VO2 +-complexes, or by an outer sphere one-electron transfer from VO2 +-complex to the second VO2 + ion. Assuming a rapid pre-equilibrium for the proton-transfer and complexation reactions, an inner-sphere electron transfer pathway has been proposed (VO2-U2+ VO2+-U•2+, k 1 = 1.4 s−1) when HU is in excess. When VO2 + in excess, an additional reaction possibly proceeds through two outer-sphere electron-transfer pathways: VO2-U2+ + VO2 + + 2H2O VO2 + + VO2+ + U, and VO2-U2+ + VO(OH)2+ + 2H2O VO(OH)2+ + VO2+ + U, characterized by k 4 = 22 s−1 mol−1 dm3, and k 5 = 3.8 × 103 s−1 mol−1 dm3.

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Abstract

The reduction kinetics with CO of the 12-molybdophosphoric—HPMo, 1-vanado-11-molybdophosphoric—HPVMo acids and their salts with NH4 +, K+ and Cs+ cations were studied for reduction/reoxidation cycles with mixtures of CO:Ar and O2: Ar, by means of “in situ” UV–Vis–DRS measurements. The reflectivity versus time curves registered during the reduction/reoxidation processes for the HPMo and HPVMo and its salts with NH4 +, K+ and Cs+ cations, at the constant wavelength of 620 nm and different reaction temperatures between 523 and 623 K, were processed as the Kubelka–Munk function versus time. The linear shape of Kubelka–Munk function versus time curves for the reduction process suggests apparent zeroth order kinetics and it was used for the calculation of apparent activation energy. The kinetic compensation effect between the apparent activation energy and the pre-exponential factor was observed. The Kubelka–Munk function versus time curves for the reoxidation process consist of two steps, the first with a very fast reaction rate and the second with a slow reaction rate. An explanation for their shape is proposed. The heteropoly oxomolybdates reach a degree of reoxidation higher than heteropoly compounds containing vanadium together with molybdenum.

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